Pattern of binding of tritiated actinomycin D to Phaseolus coccineus polytene chromosomes. II. The entire chromosome complement

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Abstract
The pattern of labelling by tritiated actinomycin D (3H-AMD) on polytene chromosomes in the embryo suspensor cells of Phaseolus coccineus is described in preparations exposed for different times to photographic emulsion. It is observed that: a) each chromosome pair displays a typical labelling pattern; b) heterochromatin close to the centromere does not label in the same way in different chromosome pairs; c) in some chromosome pairs, different bundles of strands in one an the same chromosome segment display differences in 3H-AMD labelling. These results allow an improved characterization of the Phaseolus polytene chromosomes and are discussed in relation to the possible factors determining the differential binding of 3H-AMD to the chromatin.